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Instant formatting can be very slow and if you experience this we recommend disabling this feature. You first need to have an Endnote open and a Library selected (it can be an empty library).
In Word *2003, go to Tools > Endnote X2 > Format Bibliography > Instant Formatting
In Word 2007 choose the Endnote Tab, then click on the expansion arrow in the Bibliography section.
It may take a few seconds for the next screen to appear.
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* This is for Word 2003. For Word 2007 choose the Endnote Tab, then click on the expansion arrow in the Bibliography section.